Three main factors namely global factors, population growth and the adoption of crops for biofuels create the necessity to develop novel approaches to increase crop yield. Crop productivity and yield enhancement in recent years are being achieved by genotype improvement through classical breeding, use of nitrogen fertilizer and pesticide, right agronomic way. Due to rapid population growth, income growth in developing countries, limited availability of land and climate change, achieving sustainable food security will require technological advances in agronomic practices, breeding and agricultural biotechnology (Dyson 1999, PNAS, 96(11): 5929-5936;Pinstrup-Anderson et al 1999, World Food Prospects: Critical issues for the Early Twenty-First Century, in 2020 Vision Food Policy Report). Cotton contributes natural fiber for the worldwide textile industry; therefore, dissecting its biological properties is a very important scientific objective. Although it is not easy to improve both yield and fiber quality concurrently; the yield of cotton fibers, usually known as cotton lint, is usually negatively associated with fiber quality. Aim to be achieved include increased cotton boll density, lint percentage, fiber length and strength. Presently cotton fiber quality can be improved by three types. First is by cross breeding but this method need much more time. Second is the use of fatty acids and plant hormones. Plant hormone such as Auxin or gibberellins has a promoting effect on the fiber elongation in ovule cultures {Beasley and Ting (Amer. J. Bot., 60(2): 130-139(1973), Baert et al., 1975} whereas kinetin and abscisic acid have an inhibitory effect. U.S. Pat. No. 5,880,110 produces cotton fibers with improved quality by treatment with brassinosteroids. Yong-Mei Qin et al., 2007 have reported that saturated very-long-chain fatty acids (VLCFAs; C20:0 to C30:0) exogenously applied in ovule culture medium significantly promoted cotton (Cotton) fiber cell elongation. The third one is by doing genetic manipulation. In recent years genetic manipulations have been made successful variety improvement in plants such as rice, tomato, maize etc. Therefore if a gene related with fiber development is transformed into cotton and overexpressed, it may play crucial role in the improvement of quality or yield of cotton fiber. At present, however, only the few studies have been made on cotton plants to improve the characteristics or yields of fiber such as by introduction of a BT toxin (Bacillus thuringiensis) gene into cotton to improve insect resistance, to improve herbicide (Glyphosate) resistance by introduction of 5-enol-pyruvilsshikimic acid 3-phosphate synthetase gene in cotton. There are few reports related to the method for genetically engineering a fiber producing plant and the identification of cDNA clones useful for identifying fiber genes in cotton. U.S. Pat. No. 5,597,718. Complete ORF sequence from these isolated genes is used in sense or antisense orientation to modulate the transgenic fiber producing plants. Suppression of sucrose synthase gene expression in cotton leads to reduced cell fiber length and smaller and fewer fiber cells (Yong-Ling Ruan et al, Plant Cell 15:952-964, 2003)
Identification and manipulation of specific genes in cotton that play a significant role in determining yield could provide a path to obtain substantial yield increase in a relatively short time.
SPL5 is a plant specific transcription factor which belongs to the SBP superfamily. Members of this superfamily share a highly conserved DNA binding SBP domain and are involved in various function such as flowering, early stages of microsporogenesis and megasporogenesis, development of normal plant architecture maize kernel development, tomato fruit ripeness, and shoot maturation in Arabidopsis (Cordon et. al Plant J. 1997, 12, 367-77; Unte et al, Plant Cell 2003, 15, 1009-1019; Wang et al, Nature 2005, 436, 714-719; Manning et al, Nat. Genet. 2006, 38, 948-952).
SPLs are among the transcription factors subjected to microRNA (miRNA) regulation. miR156 negatively regulates SPL gene family in Arabidopsis. miRNA originate from distinct loci within a plant's genome and are short non coding RNAs (20-24 nucleotide long) whose function is to repress the expression of defined target genes (Rhoades et al., Cell 110:513-520 110:513-520, 2002; Bonnet et al., Proc. Natl. Sci. USA, 101:11511-11516, 2004;Reinhart et al., Genes Dev. 16:1616-1626, 2002). miRNAs are produced from longer precursor molecules by a Dicer-like (DCL) ribonuclease and get incorporated into ribonucleoprotein silencing complexes that effect repression of target mRNAs via base pairing of the small RNA and its target mRNA (Chen, Science 303:2022-2025, 2004; Bao et al, Dev. Cell. 7:653-662, 2004). A number of researches have supported that SPL mRNAs are repressed by miR156 and this repression produces late flowering phenotype (Wu et al, Cell 138,750-759, 2009; Yamaguchi et al, Developmental Cell 17, 268-278, 2009).
Limitations in Prior Art
Presently no gene has been identified which causes significant increase in the boll number, size and increase in lint yield in cotton. Hence there was need to identify cotton boll density specific gene. In this present invention, we have identified a gene from Cotton which causes increase in number of cotton boll. The gene also causes significant increase in boll size and increased lint percentage. The prior art lacks identification of gene responsible for above said traits in cotton.